Such screw-and-nut fastening devices serve in particular to assemble together two or more separable parts, and they are very widespread in a variety of applications in all technical fields. To perform the operations of tightening and loosening a nut on a screw, it is necessary to prevent the screw from moving in rotation and in translation so as to ensure that it cannot turn freely, thereby failing to provide torque opposing the tightening or loosening torque exerted on the nut by some appropriate tool, such as, for example, a wrench or an automatic or semiautomatic screw-tightening machine.
When such devices are used for assembling together annular elements of a turbomachine rotor, a solution described in documents FR-A-2 502 690 and FR-A-2 715 975 consists in preventing the screws from moving in rotation and in translation by providing housings by machining or any other suitable manufacturing methods, and more particularly by providing recesses in one of the annular parts for fastening together, for the purpose of receiving screw heads shaped to co-operate with the recesses so as to prevent the screws from moving.
Nevertheless, because of the particular shape and the dimensional and positioning tolerances on the recesses, the corresponding machining is difficult and expensive to perform, particularly when the part in question is bulky, and of complex shape requiring very great precautions to be taken during handling or while performing machining operations. In addition, when the mechanical stress is applied to the part, the recesses can lead to stresses becoming concentrated within the part, thereby weakening it. To increase the strength of the part in the vicinity of such recesses, and thereby increase its lifetime, it is common to reinforce the part by adding material around the recesses, thereby ending up with an increase in the weight of the assembly. This extra weight can become a non-negligible drawback, for example in the field of aviation where it is desirable to reduce the weight of all on-board parts, or where the part is a moving part, e.g. an element of a turbocompressor or turbojet rotor, in which case it is desirable to reduce its inertia.
Another drawback of such recesses for preventing screw heads from moving is that their walls are subjected directly to the tightening torque exerted on the nut, and if that should exceed a predetermined limiting value, that can mark or even damage the part in which the recesses are formed.